Dopamine-B-hydroxylase (DBH) is a glycoprotein which catalyzes the conversion of dopamine to norepinephrine in sympathoadrenal cells. During the exocytotic release of norepinephrine, DBH protein is released and traverses via lymphatics into the circulatory pool where it maintains its enzymatic activity. In man and rat, serum DBH levels reflect poorly the activity of the peripheral sympathetic nervous system, suggesting the circulatory disposal rate for DBH, in addition to its entry rate, may be an important regulatory factor. Elucidation of the peripheral catabolic pathway for DBH would provide a firm foundation for understanding the regulation of DBH in the circulation